A head space method is a sample introduction method for heating a liquid sample or a solid sample stored in a sample container at a predetermined temperature for a predetermined period of time to volatilize components having relatively low boiling points, collecting a predetermined amount of gas containing these components from a head space (upper space) in the sample container, and introducing the gas into an analyzer. Further, a head space analysis method is a method for introducing a sample into an analyzer by the head space method to analyze the sample. A typical example of the analyzer that performs such a head space analysis method includes a gas chromatograph.
The head space method includes collecting the sample gas from the head space of the sample container to a sample loop, and introducing the collected sample gas into the analyzer. As a method for collecting the sample gas to the sample loop, the sample gas is generally collected to the sample loop when a pressure at one end of the sample loop becomes atmospheric pressure, the other end of the sample loop being connected to the head space of the sample container. However, when an inside of the sample loop is in the atmospheric pressure state, a sample component concentration may decrease, and analysis sensitivity may be insufficient.
The sample gas can be collected to the sample loop by switching a valve when the pressure inside the sample loop is a predetermined pressure before decreasing to the atmospheric pressure. In such a case, however, valve switching operation is necessary while predicting time at which the pressure inside the sample loop becomes the predetermined pressure in a state where the pressure changes with time. In addition, reproducibility of a measuring result lowers because a concentration of the collected sample gas fluctuates depending on the switching timing in such a method for switching the valve when the pressure changes.
A pressure sensor and a flow rate regulating valve, therefore, a have been provided on one end side of the sample loop having the other end connected to the head space of the sample container, and feedback control of the flow rate regulating valve has been performed by output of the pressure sensor in such a way that a back pressure on one end side of the sample loop when the sample gas is collected to the sample loop becomes a predetermined constant pressure larger than atmospheric pressure.